There was some debate spread about how the DME reacts to changes in IAT. In the most recent case, it was claimed that an IAT of approx 160 degF would result in the DME regarding timing by "3-4 degrees". Which would lead some to argue that this eliminates the desirability of active timing control in super hot conditions.

This test is easy to conduct at home as well. All you need is a .63kOhm resistor or adjustable 0-1k potentiometer (shown below). You will use it to pull down the IAT signal (pin 17 on the large black DME subconnector) to ground. When you do this, the DME will read about 95F higher.

Conclusions:
Holding all other things equal, the effects of IAT increases are huge. But not on ignition timing. But on Boost target. And not in the direction that you would want (in a tuned car). In fact, peak boost target INCREASES from only 7psi to 9.5psi. Which is why that tunes that don't offer isolated boost control see so much boost target fluctuation depending on IAT.

Holy shit. Why did the boost target go up with IAT almost double?
I'm assuming this is the factory DME.

The boost target goes up to compensates for air density reduction associated with high IATs. The idea is to keep power output reasonable constant regardless of testing conditions. Same reason that boost will go up at altitude since the DME indexes target based upon barometric readings as well.

All this is well and good for a stock car running only 6-9psi of boost. In such cases, the car is never operating aggressively. In fact, you could fairly say that the tune at moderate conditions is heavily detuned just to leave room for going more aggressive when conditions get worse.

In a tuned scenario (ie, 12psi and up), where you are already operating at or near the knock threshold, there is usually no overhead to make the tune more aggressive. In fact, you have to move in the other direction to keep the tune from being TOO aggressive when conditions take a turn for the worst.

Interesting, indeed! Of course, all this has an upper limit after which the DME will induce limp mode.

Shiv, from your personal experience, what is the upper limit here? Meaning, until what point will the stock DME continue to increase boost targets when the conditions are getting worse?

Absolutely. There is a limit as to where boost correction curve will flatten out. In fact, i believe that happens before the IAT temp levels we tested here. Easy enough to test given enough time. Most of my time was actually spent mapping out the how IAT changes effect ignition timing target. That was necessary in order to create the bit in the AutoTuning logic that calculates how aggressive the car is running at any given time.

Also, in case anyone is wondering, virtually all of the other engine parameters that have a significant influence timing target were held equal (or close to it) during these tests. This includes DME boost actual (which is equal to DME boost target courtesy of v4), coolant temp, oil temp, baro and calculated EGT. And if it wasn't clear already, knock sensor induced timing retard was also ruled out by running only 11psi with a fully modded car running a big jet to methanol at full spray pressure and 100% ignition correction via procede. Autotuning was disabled obviously.

with autotuning, that means as IAT go up, the car will drop in performance quite a lot. Does this mean on track, the first few mins we will have alot more power and itll slowly get sapped away by the end of the session as IAT increase? How can we make it more stable? (meth ?)

with autotuning, that means as IAT go up, the car will drop in performance quite a lot. Does this mean on track, the first few mins we will have alot more power and itll slowly get sapped away by the end of the session as IAT increase? How can we make it more stable? (meth ?)

You answered your own question Race gas will also have the same effect since autotuning is more influenced by historical knock retard events than IAT level.

But realistically, summer+full boost+hotlapping track days don't go hand in hand due to oil temp limitations. Which is why the Procede will reduce boost dramatically as oil temp starts to approach the scary zone.

Its funny how every time I tell people that a stock car boosts 3-4 psi higher in really hot weather they are completely shocked. Simply watching your boost gauge (everyone has one, right? ) on a stock car will shock you as you boost 5-6psi in 40F weather and 9-11psi in 100F weather.

This is why your turbos are louder on hot days...

Obviously this behavior is NOT ideal on a tuned car... as we are already past that extra boost threshold without the DME being the wiser. This is where tunes should employ some IAT based adjustments. The main piggybacks do this, PROcede retards timing, jb3 reduces boost target... but from what I have seen, flash tunes (giac stage 1 in particular from my testing) still raise boost as boost increases just like a stock tune, because most likely they were unable to modify those sections of the DME logic code, or left sufficient headroom, as the tune only boost 12psi cold, but 15psi hot.... which is leaving power on the table.

Just some food for thought...but how are the meth-less race cars able to run so aggressively without sacrificing safety (to an extent).

For example, my friend Ryan (Gates311) has a 2008 Evo X that he's had some extreme success with in the Red Line Time Attack Series (Serious Success). Long story short, his Bored/Stroked 4B11 (2.2 L inline 4) with a GT850R Turbo. He's running ~700WHP and the engine has proven to be very strong and reliable. Even when the temps are 100' F, he's running 20 minutes HARD out of the 30 minute sessions. He views meth as a 'bandaid' to fix IATs, and that the cars should just be equipped right to not need a bandaid of meth. He runs E85 fuel, and no crazy plugs/coils/exhaust/etc. Granted, his 850 turbo doesn't have to work that hard and thus probably doesn't create as much heat as our small Twins...but it still must have extremely hot IATs.

So with that example, what else can we do to better prepare our cars the 'right' way to not rely on meth?

Very interesting - good information. So what would you suggest us GIAC guys do to compensate? I'm running stage 1 and am not interested in meth but are you saying I'd get a major benefit from an intercooler?

Just some food for thought...but how are the meth-less race cars able to run so aggressively without sacrificing safety (to an extent).

For example, my friend Ryan (Gates311) has a 2008 Evo X that he's had some extreme success with in the Red Line Time Attack Series (Serious Success). Long story short, his Bored/Stroked 4B11 (2.2 L inline 4) with a GT850R Turbo. He's running ~700WHP and the engine has proven to be very strong and reliable. Even when the temps are 100' F, he's running 20 minutes HARD out of the 30 minute sessions. He views meth as a 'bandaid' to fix IATs, and that the cars should just be equipped right to not need a bandaid of meth. He runs E85 fuel, and no crazy plugs/coils/exhaust/etc. Granted, his 850 turbo doesn't have to work that hard and thus probably doesn't create as much heat as our small Twins...but it still must have extremely hot IATs.

So with that example, what else can we do to better prepare our cars the 'right' way to not rely on meth?

i think we just need more efficient turbos then that dont need to spin as fast to reach the pressures we want ..

Just some food for thought...but how are the meth-less race cars able to run so aggressively without sacrificing safety (to an extent).

For example, my friend Ryan (Gates311) has a 2008 Evo X that he's had some extreme success with in the Red Line Time Attack Series (Serious Success). Long story short, his Bored/Stroked 4B11 (2.2 L inline 4) with a GT850R Turbo. He's running ~700WHP and the engine has proven to be very strong and reliable. Even when the temps are 100' F, he's running 20 minutes HARD out of the 30 minute sessions. He views meth as a 'bandaid' to fix IATs, and that the cars should just be equipped right to not need a bandaid of meth. He runs E85 fuel, and no crazy plugs/coils/exhaust/etc. Granted, his 850 turbo doesn't have to work that hard and thus probably doesn't create as much heat as our small Twins...but it still must have extremely hot IATs.

So with that example, what else can we do to better prepare our cars the 'right' way to not rely on meth?

Hi Brian,
The reason that Ryan doesn't run hot without alcohol injection is because he is essentially E85 which is effectively the same thing we fill up our methanol bottles with. So instead of using it as a supplement to standard gasoline injection (as we are doing), he is running it instead of gasoline injection. So he gets all the cooling and octane advantages that we do (if not more). The downside is that e85 isn't readily available and results in 30-40% more fuel consumption.

Ryans;s car would run MUCH hotter if he had to run gasoline. In that case, he's probably find himself running some sort of meth injection

We built an e85 powered Evo IX for Mitsubishi Motors a few years ago. Drove great and ran cool regardess of how hot it got! But I had to fill up the tank nearly 3 times for a 350mile drive to LA for the LA Auto Show.

Hi Brian,
The reason that Ryan doesn't run hot without alcohol injection is because he is essentially E85 which is effectively the same thing we fill up our methanol bottles with. So instead of using it as a supplement to standard gasoline injection (as we are doing), he is running it instead of gasoline injection. So he gets all the cooling and octane advantages that we do (if not more). The downside is that e85 isn't readily available and results in 30-40% more fuel consumption.

Ryans;s car would run MUCH hotter if he had to run gasoline. In that case, he's probably find himself running some sort of meth injection

We built an e85 powered Evo IX for Mitsubishi Motors a few years ago. Drove great and ran cool regardess of how hot it got! But I had to fill up the tank nearly 3 times for a 350mile drive to LA for the LA Auto Show.

That makes sense, and that build looks really cool! So aproximately how much cooler do you think the cylinder temps and EGTs are with E85? I wish our fuel system could flow the necesary fuel to run E85... Thanks You1